In the field of industrial automation technology, electrical loads (for example an electric motor) are connected to a power supply network for the supply of power. The power supply network is, in particular, a low voltage network.
In the voltages generally used in low voltage networks in Europe, the nominal value of the star voltage is 230 volts. For controlling an electrical load, the power supply to the electrical load is conducted via a switchgear so that the load is able to be controlled thereby. The switchgear is thus connected on the input side to the power supply network and is connected on the output side to the electrical load. In the case of electric motors, such switchgears are generally motor starters.
If the power supply network is a three-phase alternating current network and the consumer is a three-phase motor, a three-phase alternating current is applied to the consumer. The three-phase alternating current is conducted to the consumer via the switchgear, in particular via the three current paths thereof, so that the switchgear operates in three-phase operation. In standard operation, with three-phase alternating current, three separate alternating currents and/or alternating voltages of the same frequency are present and have a fixed phase shift of 120° relative to one another. An alternating current is an electrical current which alters its direction (polarity) in regular repetition and in which positive and negative instantaneous values complement one another so that the current in the temporal mean is zero.
If the consumer is a single-phase motor, one phase of the three-phase alternating current network is generally conducted to the single-phase motor via the individual current paths of the switchgear. The switchgear operates in single-phase operation.
In electronic switchgears for motorized and non-motorized loads, it is advantageous to identify different network errors, such as phase failure, phase overload and phase unbalance in order to switch off the load in this case and to communicate the error to the operator. Such errors may be the absence of individual phases, a plurality of phases or all three phases. The identification of interruptions to individual motor conductors or a plurality of motor conductors is also incorporated therein.
To determine such network errors, unbalances and cases of overload, voltage values and current values of the individual phases are generally detected and evaluated by the interposed switchgear.